The open race valve vents the air directly to the atmosphere, which can make a loud noise. Depending on where the race valve is located, it can also kick up a lot of road dust. The enclosed race valve is designed to enable a hose to be clamped to it, this allows the air to either be run back into the system or dumped wherever the installer desires. Routing the hose past the firewall quiets down the release of air from the valve.
